Oxygen (interstitial oxygen) is considerably mixed into a silicon single crystal produced by means of a Czochralski (CZ) method due to the use of a quartz crucible. It has been known that this oxygen is to become precipitates during crystal production and during heat treatment in a device fabrication process subsequent to slicing the crystal into wafers and processing the wafers.
If crystal defects such as oxide precipitates reside in a device active region, the crystal defects work as a cause for reducing device yields; therefore, it is necessary to form as a device active region a so-called DZ layer where crystal defects are eliminated. On the other hand, if BMDs such as oxide precipitates have been generated in the inside (a bulk portion) of a substrate, the defects bring about an improvement effect of gettering capability for heavy metal impurities. From these viewpoints, it is very important to control an amount of oxide precipitates (control of oxygen precipitation characteristics) in a silicon wafer.
DZ layer width and BMD density are in an inverse correlation; it has been known heretofore that simultaneous increase in BMD density and DZ layer width is impossible in any kind of single stage heat treatment.
While, in recent years, as heat treatment for increase in BMD density, heat treatment using a rapid heating-rapid cooling apparatus (such heat treatment is hereinafter referred to as RTA: Rapid Thermal Annealing) has been known (for example, U.S. Pat. No. 5,994,761). The fact of decrease in DZ layer width with increase in BMD density still remains unavoidable in RTA similarly to prior art heat treatment; there arises difficulty in fabrication and design of a device.